Friction winding shaft

ABSTRACT

A friction winding shaft has a shaft body ( 12 ) and a plurality of friction rings ( 14 ), which can be driven in slaved fashion by the shaft body. By means of the friction rings ( 14 ), bushes ( 24 ) for winding operations can be driven in slaved fashion, and between the shaft body ( 2 ) and the friction elements ( 14 ), radially movable friction elements ( 28 ) are provided, which can be pressed by means of positioning elements ( 30 ) against inner circumferential surfaces ( 32 ) of the friction rings ( 14 ). In order to achieve the least possible fluctuations in the frictional moment between the shaft body and the friction ring, it is proposed that between the shaft body ( 12 ) and the friction rings ( 14 ), an air gap ( 34 ) is provided, and on the outer face of the shaft body ( 12 ), at least two slide elements ( 36 ) are provided, which rest on inner surfaces ( 32 ) of the friction rings ( 14 ).

Friction winding shafts have a shaft body and a plurality of friction rings, which can be slaved in friction-locking fashion by the shaft body; by means of the friction rings, bushes, for instance of cardboard or plastic, for winding operations can be driven in slaved fashion, and between the shaft body and the friction rings, radially movable friction elements are provided, which can be pressed against inner circumferential surfaces of the friction rings by means of positioning elements.

Such shafts are used for winding up windings of different diameters. The friction rings make differences in rotary speed possible between a plurality of rolls disposed next to one another on a shaft. The shaft fundamentally rotates faster than the synchronous rpm necessary for the smallest roll. The positioning elements are as a rule embodied as flat hoses that can be subjected to compressed air and that are seated on the base of axially extending grooves in the outer surface of the shaft body. When compressed air is applied, these hoses then press the rubbing strips, which are normally located retracted in the shaft and spaced apart from the friction rings, radially outward against an inner circumferential surface of the friction rings. The slaving of the friction rings is then effected as a result of the frictional forces built up. One example of a friction winding shaft of this kind is known from German Patent Disclosure DE 195 15 723 A1.

In order to center the friction rings on the shaft body and guide them in the direction of rotation, a fit is provided between the outer face of the shaft body and the inner surface of the friction ring; although high demands in terms of precision cannot be made of this fit, nevertheless these demands require a certain amount of production effort and expense. Over longer-term operation, however, it is more problematic that residues, for instance from a lubricant used for the friction elements, or abrasion of the friction elements in the gap between the shaft body and the friction ring, can become stuck, as a result of which the frictional moment and thus also the quality of the winding vary. In particular, as a result, over the course of time the drag moment can increase markedly, even with hoses not subjected to air pressure. In the worst case, wear marks can occur, which considerably change the coefficients of friction of the friction pairing.

Finally, there is also the risk that lubricant will be carried to the outside by centrifugal force and can soil the material being wound.

The object of the present invention is to create a friction winding shaft which over its useful life has lesser fluctuations in the moment of friction between the shaft body and the friction ring.

According to the invention, the object is attained by a friction winding shaft of the type defined at the outset in which between the shaft body and the friction rings, an air gap is provided, and on the outer face of the shaft body, at least two slide elements are provided, which rest on inner surfaces of the friction rings.

The advantage of this achievement of the invention is that the central guidance of the friction rings is now taken on by the especially provided slide elements, so that the fit provided over the entire circumference in earlier embodiments between the metal shaft body and the friction rings can be dispensed with. The slide elements can be of plastic; suitable plastics are known, such as bearing bushes of plastic, for instance PBT, PTFE, and mixture forms, or other polymers. The width of the air gap between the shaft body and the friction ring is on an order of magnitude of up to a few millimeters, for instance, preferably in a range from approximately 0.1 mm to 1 mm. Thus the play between the shafts and the friction rings is too great for the friction rings to be able to be guided directly by the shaft in the direction of rotation. The guidance is accomplished solely by means of the slide elements, which are not present in the prior art. When there are only two slide elements, they should ideally be disposed diametrically opposite one another on the shaft body and extend over a certain minimum angle.

In a preferred embodiment of the invention, it is provided that the slide elements slide dry on the inner surfaces of the friction rings. In this embodiment, the accumulation of lubricant residues is prevented entirely, and the advantage is thereby attained that suitable plastics are available on the market that permit slide bearing without lubricant additives, which is otherwise indispensable in a metal-to-metal pairing.

The slide elements are preferably disposed between the friction elements, and two or more slide elements can also be provided between the friction elements. Therefore the result is a number of slide elements that is equivalent to the number of friction elements, or a multiple thereof. Embodiments which provide three or six slide elements for three existing friction elements are preferred.

The disposition of the slide elements can also be done in such a way that U-shaped slide strips are provided, and the rubbing and positioning elements are disposed between the legs of the slide strips, and the ends of the legs form the slide elements. Accordingly, in this embodiment, if three friction elements are provided, there are six slide elements.

In a particular embodiment of the invention, it may also be provided that the slide elements and the friction elements are embodied in one piece, and they are disposed in axial grooves in the shaft body, which form shoulders that in the retracted position ensure contact with the friction rings. This embodiment makes do with especially few parts, but it does require somewhat greater effort and expense in adapting the positioning forces of the positioning elements and in the choice of a suitable plastic, which has a sufficiently high coefficient of friction to be capable of transmitting the requisite driving moments to the friction rings. In particular, a precise depth of the shoulders in the shaft body must also be adhered to, to ensure the contact of the rubbing bodies with the friction rings even whenever no positioning forces are operative. As a result, in this embodiment, despite the air gap, the guidance exists in all operating states, despite the rubbing/slide element that is embodied in one piece.

In this embodiment, it is possible for only some of the combined slide/friction elements to be provided with a positioning element, for instance only one combined slide/friction element. Then, when pressure is exerted as a result of the forces of reaction, the other slide/friction elements, without a positioning element, are pressed against the inner surfaces of the friction rings.

Exemplary embodiments of the invention are described below in conjunction with the accompanying drawings. In the drawings:

FIG. 1 shows a first embodiment of a friction winding shaft;

FIG. 2 shows a further embodiment of a friction winding shaft without a winding;

FIG. 3 shows still another embodiment of a friction winding shaft;

FIG. 4 shows an embodiment of a friction winding shaft with combined slide/friction elements.

In FIG. 1, a friction winding shaft 10 is shown, which has both a centrally driven shaft body 12 and a friction ring 14 that has an inner ring 16 and an outer ring 18. The outer ring 18, which is rotatably relative to the inner ring 16, in combination with a plurality of balls 20 that are provided and run on oblique faces 22, makes it possible to clamp a bush 24 in place, for instance of cardboard or plastic, onto which a winding 26 is to be wound, such as cut paper material. Such friction winding shafts are used for winding paper rolls and rolls of high-quality films or foils. The friction rings 14, a plurality of which are disposed parallel to and next to one another on the shaft body 12, act as a kind of slip coupling, so that windings 26 of different diameters can be wound up onto one common shaft. The transmission of the requisite drive moments from the shaft body 12 onto the friction ring 14 is effected by frictional moments, and the requisite frictional forces are generated by friction elements 28, which, with the interposition of guard strips 29 of positioning elements 30, can be pressed radially outward against an inner surface 32 of the inner ring of the friction ring 14. The positioning elements 30 comprise flat hoses, which can be subjected to an air pressure, so that the driving action can be switched on by subjection to the air pressure.

As described thus far, the friction winding shaft 10 shown corresponds to the prior art in DE 195 15 723 A1; for the applicable details, the disclosure content of this document is expressly referred to.

In the case of the friction winding shaft 10, it is novel that the shaft body 12 is made with an outer diameter that does not form a play pairing with the inner diameter 32 of the inner ring of the friction rings 14, but instead is embodied as markedly smaller, so that in the exemplary embodiment shown, a width of a gap 34 between the shaft body 12 and the friction ring 14 that can amount to up to 1 mm results. Fundamentally however, the absolute height of the gap 34 is not critical; that is, still other gap heights are optionally possible as well. Good results have been gained with a diameter of the shaft body 12 that is approximately 0.5 mm to 1 mm smaller than the inner diameter of the inner ring 16.

In order nevertheless to support the friction rings centrally on the shaft body 12, slide elements 36 in the form of strips are provided, which are disposed between the friction elements 28. In the exemplary embodiment shown in FIG. 1, two slide elements 36 are disposed between each of the friction elements. The slide elements 36 are seated in corresponding axial grooves 38 in the outer circumference of the shaft body 12. The depth of the grooves 38 is adapted to the height of the sliding elements 36 in such a way that the sliding elements slide without play by their radial outer surfaces on the inner surface 32 of the inner ring. The slide elements 36 comprise suitable plastics, of the kind used for instance in slide bearing bushes of plastic. The slide elements 36 run dry, without lubricant additives, on the inner surface 32, so that no contamination that could accumulate in the gap 34 or emerge between the friction rings 14 and'soil the winding is to be expected.

A further embodiment of a friction winding shaft 110 is shown in FIG. 2. The friction rings 14 are equivalent to the embodiment described above, except that the embodiment of striplike slide elements 136, which are disposed in correspondingly shaped axial grooves 138 in the shaft body 112, differs from the embodiment described above. As can be seen, the slide strips 136 are disposed centrally between the friction elements 28, with only one slide element 136 provided between each of the friction elements 28. The width of the gap 34 is equivalent to the embodiment described above.

In FIG. 3, a further embodiment of a friction winding shaft 210 is shown, in which the friction rings 14 are again equivalent to the embodiment of FIG. 1.

In a shaft body 212 in this embodiment, suitably enlarged axial grooves 238 are provided, in which U-shaped sliding bodies 235 are disposed, whose legs 237 on their ends form the slide elements 236. Between the legs 237 there is space for both the friction elements 28 and the positioning elements 30, the latter again being embodied as flat hoses and both structurally in turn corresponding to the friction and positioning elements 28, 30 shown and described in FIG. 1.

Finally, in FIG. 4, an embodiment of a friction winding shaft 310 is also presented, in which combined slide/friction elements 336 are provided, which are disposed in suitably shaped axial grooves 338 in the shaft body 312. Air hoses as positioning elements 30 again serve to press the combined slide/friction elements 336 radially outward against the inner surface 32 of the inner ring 16 of the friction rings 14 and thus to provide for a buildup of the friction moments. It is important in this embodiment that the slide/friction elements 336 rest on shoulders 339, embodied laterally of the positioning elements 30, when the positioning elements 30 are inactive. As a result, the guidance of the friction rings 14, which must be accomplished by the slide/friction elements 336 because of the widened air gap 34, is ensured. 

1. A friction winding shaft, having a shaft body and a plurality of friction rings, which are drivable in slaved fashion in friction-locking fashion by the shaft body, and by means of the friction rings, bushes for winding operations can be driven in slaved fashion, and between the shaft body and the friction rings, radially movable friction elements are provided, which can be pressed by means of positioning elements (30) against inner circumferential surfaces of the friction rings, wherein between the shaft body and the friction rings, an air gap is provided, and on the outer face of the shaft body, at least two slide elements are provided, which rest on inner surfaces of the friction rings.
 2. The friction winding shaft of claim 1, wherein the slide elements are of plastic.
 3. The friction winding shaft of claim 1, wherein the slide elements (36; 136; 236; 336) slide dry on the inner surfaces (32) of the friction rings (14).
 4. The friction winding shaft of one of claim 1, wherein the slide elements are disposed on the circumference between the rubbing elements.
 5. The friction winding shaft of claim 4, wherein two or more slide elements each are disposed between the friction elements in spaced-apart fashion.
 6. The friction winding shaft of one of claim 1, wherein three or six slide elements are provided.
 7. The friction winding shaft of claim 5, wherein the U-shaped sliding bodies are provided, and the rubbing and positioning elements are disposed between legs of the sliding bodies, and the ends of the legs of the sliding bodies form the slide elements.
 8. The friction winding shaft of one of claim 1, wherein the slide elements and the friction elements are embodied in one piece and are disposed in axial grooves in the shaft body that form shoulders, which in the retracted position ensure contact with the friction rings.
 9. The friction winding shaft of claim 8, wherein only some of the combined slide/friction elements are provided with a positioning element. 